Copolymerization and/or compounding of vinyl halide polymer compositions is necessary because of the limitations of vinyl halide homopolymers. One such limitation is the difficulty encountered in processing vinyl halide homopolymers at elevated temperatures. Processing of vinyl halide homopolymers on mill rolling banks can be improved by blending with acrylic copolymer processing aids as previously referred to. While acrylic copolymer processing aids improve the rolling bank and other processing characteristics of vinyl halide compositions during mill processing, usual fabrication temperatures for rigid vinyl halide polymer compositions can lead to thermal degradation of these compounds during extended fabrication periods, for instance during extrusion, injection, thermal forming, blow molding and the like.
It is common to employ certain compounds such as organic ester plasticizers to flexibilize vinyl halide polymer compositions at service temperatures. Such additives reduce the melt viscosity of the vinyl halide polymer, but adversely affect the heat deflection temperature at elevated temperatures. The improvement in processing characteristics without reduction in heat deflection temperature of the vinyl halide graft copolymer at elevated temperatures is only one deficiency of such compositions which is improved by the incorporation of the polyesters of the invention.
Another example of a limitation of the vinyl halide polymers is low impact strength. While graft copolymerizing vinyl halide monomers in the presence of olefin polymers provides compositions having good impact strength, the vinyl halide graft copolymer composition is opaque. It has now been discovered that the polyesters of the invention form homogeneous compositions with vinyl halide graft copolymers based on olefin polymers which exhibit improved impact strength over such vinyl halide graft copolymers. The incorporation of the polyesters of the invention in addition provides a means of modifying vinyl halide graft copolymers to improve impact strength without reducing the heat deflection temperature at elevated temperatures. Depending upon the amount of the polyester of the invention contained in homogeneous compositions of polyester and vinyl halide graft copolymer compositions of the invention, the heat distortion temperature can even be increased. The polyesters of the invention in blends with vinyl halide graft copolymers also act to improve the processing characteristics and reduce melt viscosity.